The present invention relates to an adhesive tape comprising a biaxially stretch-oriented polypropylene base film and an adhesive layer. Also, the invention relates to a method for making this tape.
Adhesive tapes based on plastics have been known for a long time. Films most frequently employed are composed of polyvinyl chloride or polypropylene. For this field of use, polypropylene films have the advantage, compared with polyvinyl chloride films, of better resistance to low temperatures, better capacity to withstand heat and lower density and, hence, a lower price per unit area. Disadvantages, in comparison with polyvinyl chloride films, are an inferior pattern of properties in the longitudinal direction, relatively poor printability, the necessity of applying a release coat in an off-line process and/or the necessity of applying an adhesion-promoting layer for the adhesive layer of the adhesive tape and also the considerable and annoying noise of unrolling when the coated film webs are cut into adhesive tapes and when the adhesive tapes are used.
Various possible means of eliminating these individual disadvantages of polypropylene films have already been indicated in the relevant patent literature. However, the individual patent applications and patents only concern themselves with overcoming, in each case, only one disadvantage of those mentioned. For example, German Offenlegungsschrift No. 3,144,911 describes an adhesive tape compossed of a biaxially stretched (oriented) polypropylene base film and an adhesive layer applied on at least one side. No adhesion-promoting layer for the adhesive is required by virtue of the polypropylene base film having been modified with a natural or synthetic resin having a softening point of 70.degree. to 170.degree. C.
A polypropylene film or a polypropylene adhesive tape which does not exhibit any of the disadvantages mentioned above is not yet known.